MICROMACHINED FLOW SWITCHES

Abstract: The micromachined flow switches are capable of accurately handling substantially continuous fluid flow rates as low as about 0.01 cc/day. The flow switches are so miniaturized, corrosion-resistant and non-toxic that they are suitable for being implanted in the human body; and are capable of being mass produced at costs so low, by using micromachining techniques, such as etching, that they may be considered to be disposable. The flow switches are passive devices which consume no electrical energy at all. The flow switches are reliable because they may have as few as only two parts, only one which is a moving part; and because they may handle fluids at very low pressures.

Description: MICROMACHINED FLOW SWITCHES BACKGROUND OF THE INVENTION The present invention relates to fluid handling devices. More particularly, it relates to reliable, accurate, flow switches which are capable of handling fluid flow rates which are so low that they may be measured in hundredths of a cubic centimeter per day; which may have a zero electrical energy consumption; and which may be economically mass produced by using micromachining processes. SUMMARY OF THE INVENTION In many medical situations, it is desirable to continually administer fluid medication to a patient over an extended period of time at a relatively low flow rate. Examples of such cases are the use of morphine for the treatment of malignant or non-malignant pain; the use of FTJDR for cancer chemotherapy; and the use of baclofen for the treatment of intractable spasticity. This manner of administering the medication is desirable because the level of the fluid medication in the patient's blood remains at a relatively constant, medically effective level. By way of contrast, if the medication was administered periodically in larger doses, such as in tablet form by mouth, the level of the medication in the patient's blood may tend to fluctuate markedly over time, from too little to too much, rather than staying at the desired medically effective level. Accordingly, one general aspect of the present invention may be to provide flow switches which are capable of continually handling fluids over an extended period of time at relatively low flow rates, which may be as low as about 0.01 cc/day. In many medical situations it is desirable to have flow switches which are extremely small, so that they may be implanted within a patient's body. Accordingly, another general aspect of the present invention may be to provide flow switches which are so small that they may be easily implanted within a patient's body. However, when making a flow switch which is so small, it becomes relatively easy to inadvertently clog any openings in the flow switch (such as its ports, channels, cavities, or gaps) if a bonding material is used to bond the various parts of the flow switch together. Accordingly, another general aspect of the present invention is to provide flow switches in which at least some of their parts are anodically bonded together, thereby eliminating the need to use a separate bonding material to bond those parts together. If the flow switches are intended to be implanted in a patient's body, it is preferable that they be passive devices, which do not consume any electrical energy at all. In medical situations, the reliability of the flow switches which handle the fluid medication must be very high. In general, reliability may be enhanced by simplifying the flow switches to have as few total parts as possible; to have as few moving parts as possible; and to have nominal operating pressures which are as low as possible. Accordingly, one general aspect of the present invention may be to provide flow switches which are inherently highly reliable because they may have a total of as few as two parts, as few as one of which may be a moving part. Another general aspect of the present invention may be to provide flow switches which may operate at relatively low operating pressures. In medical situations, it is desirable to have flow switches which have a fail-safe design so that if they are subjected to overpressures in excess of their nominal design limits, they are very resistant to failure, so that they do not deliver excessive amounts of the medication to the patient. Accordingly, another general aspect of the present invention may be to provide flow switches which, when subjected to an overpressure, may be resistant to being ruptured because their flexures or membranes may be at least partially supported by at least one other element of the flow switches; and which may reduce the flow of the medication, or shut it off altogether. In view of the generally high cost of medical care, it is desirable to provide high quality, accurate, reliable flow switches at a price which is so economical that the flow switches may be considered to be disposable. Accordingly, another general aspect of the present invention may be to achieve these goals by using micromachining processes to mass produce the flow switches, or parts thereof. Since many medications and body fluids are corrosive, particularly where the flow switch is used for an extended period of time, or is implanted in a human or an animal, it is important that the flow switch be corrosion-resistant. Accordingly, three further general aspects of the present invention may be to provide a flow switch having a layer of one or more corrosion-resistant substances; to bond such a corrosion-resistant layer to the flow switch by using anodic bonding; and to automatically perform such anodic bonding of the corrosion-resistant layer at the time certain other parts of the flow switch are being anodically bonded together. In many medical situations, it may be desirable to automatically switch off the flow of the medication to a patient if the medication exceeds a predetermined pressure or flow rate, in order to prevent the patient from receiving an overdose of the medication; and to automatically switch the flow of the medication back on, once the pressure of the medication falls below that predetermined pressure. Accordingly, in addition to one or more of the above general aspects of the present invention, a specific aspect of the present invention may be to provide a flow switch which will automatically switch off the flow of the medication through the flow switch in the event the medication exceeds a predetermined pressure or flow rate, and which will automatically switch the flow of the medication through the flow switch back on once the pressure of the medication falls below that predetermined pressure. Such a flow switch may comprise a substrate having a inlet switch seat, and outlet means. The flow switch may further comprise a membrane secured to the substrate, wherein the membrane's mounting portion is secured to the substrate, the membrane's flexure extends partially over the inlet switch seat, and the flexure's inlet port is located over the inlet switch seat. A switch gap is located between the flexure and the switch seat. During use, the flexure's top surface and the inlet port are exposed to a source of the medication under pressure. The medication will flow sequentially through the inlet port, radially outwardly across the switch seat's top surface in the switch gap, and out through the outlet. As the driving pressure difference (P) of the medication across the flow switch is increased from zero, the medication gradually forces the flexure closer to the switch seat, thereby gradually decreasing the height of the switch gap (and vice versa) . Then, at a predetermined overpressure of the medication, i.e., at a predetermined driving pressure difference switch point (P sw ) , the flexure automatically begins an irreversible collapse that results in the flexure being forced by the medication against the inlet switch seat, and being held there by the medication, thereby automatically closing the switch gap, switching off the flow switch, and stopping the flow of the medication through the flow switch. Then, when the driving pressure difference (P) across the flow switch is decreased to less than the predetermined overpressure, i.e., is decreased to less than the driving pressure difference switch point (P sw ) , the resiliency and elasticity of the flexure cause it to automatically move away from the inlet switch seat, thereby automatically opening the switch gap, switching the flow switch back on, and permitting the medication to flow through the flow switch once again. Although all of the forgoing comments regarding the flow switches of the present invention have been with reference to handling medicinal fluids in a medical context, it is understood that the flow switches of the present invention may also be used to handle any type of non-medicinal fluid, in both medical and non-medical contexts. In addition, although the flow switches which were mentioned above may be very small and may handle fluids at very low flow rates and at relatively low pressures, it is understood that, by applying scaling laws, the flow switches of the present invention may, in general, be scaled up to any desired size; to handle any desired fluid flow rate and pressure. Further, the term "fluid" is used in its broad sense, and includes both liquids and gasses. It should be understood that the foregoing summary of the present invention does not set forth all of its features, advantages, characteristics, structures, methods and/or processes; since these and further features, advantages, characteristics, structures, methods and/or processes of the present invention will be directly or inherently disclosed to those skilled in the art to which it pertains by the following, more detailed description of the present invention. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a top elevational view of a micromachined radial flow regulator; Fig. 2 is a cross-sectional view thereof, taken substantially along line 2 - 2 of Fig. 1; Fig. 3 is a graph depicting certain of the fluid flow characteristics thereof; Fig. 4 is a schematic diagram of some of the fluid characteristics thereof; Figs. 5 and 6 are graphs depicting certain further fluid flow characteristics thereof; Fig. 7 is a perspective view, partly in a cross- section taken substantially along line 7 - 7 of Fig. 8, of a micromachined linear flow regulator having a contoured regulator seat; Fig. 8 is a top elevational view thereof; Figs. 9 - 11 are top elevational views of three additional embodiments thereof; Fig. 12 is top plan view of a first embodiment of the micromachined one-way valve; Fig. 13 is a cross-sectional view thereof, taken substantially along line 13 - 13 of Fig. 12; Fig. 14 is a cross-sectional view thereof, taken substantially along line 14 - 14 of Fig. 12; Fig. 15 is top plan view of a second embodiment of the micromachined one-way valve; Fig. 16 is a cross-sectional view thereof, taken substantially along line 16 - 16 of Fig. 15; Fig 17 is a cross-sectional view thereof, taken substantially along line 17 - 17 of Fig. 15; Fig. 18 is a schematic representation of certain factors used in a mathematical model thereof; Fig. 19 is a top plan view of a third embodiment of the micromachined one-way valve; Fig. 20 is a cross-sectional view thereof, taken substantially along line 20 - 20 of Fig. 19; Fig. 21 is a cross-sectional view of the micromachined membrane flow switch 250 of the present invention, taken substantially along line 21 - 21 of Fig. 22; Fig. 22 is a top elevational view thereof; and Figs. 23 - 26 are graphs depicting certain fluid flow characteristics thereof. DESCRIPTION OF THE PREFERRED EMBODIMENTS MICROMACHINED RADIAL FLOW REGULATOR 32 (FIGS. 1 - 6): OPERATION AND DESIGN The radial flow regulator 32 may be installed in its intended location of use in any suitable way. Any suitable medication supply means may be used to connect the radial flow regulator 32's inlet channels 38 to a source of the medication 12; and any suitable medication delivery means may be used to connect the radial flow regulator 32's outlet port 54 to whatever person, animal or thing is to receive the medication 12 from the outlet port 54. In some cases, the medication supply means may also be used to supply the medication 12 to the flexure 28's top surface 62, at a pressure which may or may not be the same as the pressure at which the medication 12 is supplied to the inlet channels 38. For example, the radial flow regulator 32 may be installed within any type of reservoir means for the medication 12 by any suitable means, such as by locating the radial flow regulator 32's outlet port 54 over the reservoir means's outlet, and by using an adhesive face seal between the radial flow regulator 32's bottom surface 56 and the inside of the reservoir means to hold the radial flow regulator 32 in place. As a result, when the reservoir means is filled with the medication 12, the radial flow regulator 32 will be immersed in the medication 12, with its inlet channels 38 and its flexure 28's top surface 62 in fluid communication with the medication 12 within the reservoir means, and with its outlet port 54 in fluid communication with the reservoir means' outlet. Such an installation for the radial flow regulator 32 has numerous advantages. For example, it is quick, easy, reliable and inexpensive, because no additional medication supply means (such as supply conduits) are needed to supply the medication 12 to the radial flow regulator 32's inlet channels 38 and to the flexure 28's top surface 62 (since they are already immersed in the medication 12) ; and because no additional medication delivery means (such as delivery conduits) are needed to convey the medication 12 away from radial flow regulator 32's outlet port 54 (since the reservoir means' outlet is used for this purpose). Such additional inlet and outlet conduits may be undesirable since it may be relatively time consuming, difficult and expensive to align and connect them to radial flow regulator 32, due to the extremely small size of its inlet channels 38, flexure 28, and outlet port 54. Such additional inlet conduits may also be undesirable because they may tend to trap a bubble when being filled with a liquid medication 12, which bubble might then be carried into the radial flow regulator 32 and cause it to malfunction. In the discussion which follows it will be assumed, for clarity and simplicity, that during operation of the radial flow regulator 32, the flexure 28's top surface 62 and the entrances of the inlet channels 38 are all exposed to a pressurized source of the medication 12 from the medication supply means. It will also be assumed, for clarity and simplicity, that the driving pressure difference (P) of the medication 12 across the radial flow regulator 32 is the pressure difference between the medication 12 at the membrane 36's top surface 62, and the medication 12 at the outlet port 54; which is the same as the pressure difference between the medication 12 at the entrances of the inlet channels 38 and the outlet port 54. However, it is understood that during operation of the radial flow regulator 23, these pressure differences need not be equal, and the flexure 28's top surface 62 does not necessarily have to be exposed to the pressurized source of the medication 12 from the medication supply means. When the flexure 28's top surface 62 is exposed to the medication 12, the driving pressure difference (P) across the flexure 28 may be the dominant factor in determining the amount of deflection of the flexure 28, and thus, the size of the regulator gap 48. On the other hand, if the flexure 28*s top surface 62 is not exposed to the medication 12, then the velocity of the medication 12 through the regulator gap 48 may be the dominant factor in determining the amount of the deflection of the flexure 28, and thus, the size of the regulator gap 48. During operation, as a driving pressure difference (P) is applied across the radial flow regulator 32, such as by pressurizing the source of the medication 12 with respect to the radial flow regulator 32's outlet port 54 by any suitable means, the medication 12 will pass sequentially through the radial flow regulator 32's inlet channels 38, inlet cavity 40, regulator gap 48, outlet cavity 52, and outlet port 54. The inlet cavity 40 may serve to more or less equally distribute the flow of the medication 12 from the inlet channels 38 to the entire circumference of the regulator gap 48, for more predictable operation of the radial flow regulator 32. Referring now to Fig. 3, the regulator curves 64, 66, 68 and 70 are illustrated for a radial flow regulator 32 having one, two, three and four radial inlet channels 38, respectively. The triangular, diamond, circular and square data points on the regulator curves 64, 66, 68 and 70 are for the measured flow rate (Q) of an actual radial flow regulator 32 having the physical parameters of the example radial flow regulator 32 which was set forth above. The regulator curves 64, 66, 68 and 70, as well as all of the data points in Fig. 3, are plots of the flow rate (Q) of the medication 12 through the radial flow regulator 32 in microliters per day (μL/day) , as a function of the driving pressure difference (P) across the radial flow regulator 32 in millimeters of mercury (mm Hg) . As seen in Fig. 3, at a zero driving pressure difference (P) there is no flow of the medication 12 through the radial flow regulator 32, regardless of how many inlet channels 38 there may be. Then, as the driving pressure difference (P) is increased from zero, the radial flow regulator 32 exhibits four flow regimes, again regardless of the number of inlet channels 38 which it may have. That is, as the driving pressure difference (P) is increased from zero, there is a corresponding increase of the flow rate (Q) ; but there is also a gradual lessening of the flow rate's (Q's) sensitivity to the driving pressure difference (P) . For example, this is seen on the curve 66 from about a 0 mm Hg to about a 200 mm Hg driving pressure difference (P) . At intermediate driving pressure differences (P) there is a "control zone" wherein the flow rate (Q) is relatively insensitive changes in the driving pressure difference (P) . For example, this is seen on the curve 66 from mm Hg to about 300 mm Hg. Then, at driving pressure differences (P) higher than the "control zone", the flow rate (Q) actually decreases as the driving pressure difference (P) increases. For example, this is seen on the curve 66 from about 300 mm Hg to about 450 mm Hg. Finally, at very high driving pressure differences (P) , not illustrated in Fig. 3, the flow rate (Q) may gradually decrease to near zero as the driving pressure difference (P) of the medication 12 acting on the flexure 28's top surface 46 drives the flexure 28 down against the regulator seat 42. It has been discovered that the radial flow regulator 32 has a built-in, fail-safe characteristic, due to its structure, that may provide the user with exceptional protection against catastrophic failure of the flexure 28, when the flexure 28 is subjected to driving pressure differences (P) that are far in excess of the regulator 32's designed driving pressure difference (P) range. This fail-safe characteristic exists because, as has been mentioned, at very high driving pressure differences (P) the medication 12 acting on the flexure 28's top surface 46 may drive the flexure 28 down against the regulator seat 42's top surface 44. When this happens, the regulator seat 42 then acts as a support for the flexure 28 and prevents its further downward deflection; which further deflection might otherwise cause the flexure 28 to crack or rupture. As a result, a much higher driving pressure difference (P) is required to rupture the flexure 28 than would otherwise be the case, since the largest unsupported span of the flexure 28 is reduced in size from the maximum overall diameter of the inlet cavity 40, to the much smaller radial width of the ring-shaped inlet cavity 40. For example, for a flexure 28 which was a membrane of silicon about 25 microns thick, a driving pressure difference of at least about 100 psi (5,171 mm Hg) would be required to crack or rupture the flexure 28. By way of comparison, as seen in Fig. 3, the regulator 32's typical operating driving pressure difference (P) may be only about 300 mm Hg. Thus, in this instance, the regulator 32 would have about a 17 times overpressure safety factor. The type of response curves 64, 66, 68, 70 shown in Fig. 3 is highly desirable for many applications. This is because the radial flow regulator 32 will deliver a relatively constant flow rate (Q) of the medication 12 in its nominal "control zone", despite a substantial range of variations in the driving pressure difference (P) . In addition, if the nominal "control zone" driving pressure difference (P) is exceeded, then the flow rate (Q) of the medication 12 will not increase, but will actually decrease; thereby avoiding the possibility of damage which might otherwise be caused if the flow regulator 32 permitted more than the desired amount of the medication 12 to flow. For example, let us assume that a medication delivery device, having a source of medication 12 under pressure, was equipped with a radial flow regulator 32 in order to control the flow rate (Q) of the medication 12 from the medication delivery device. As a result, such a medication delivery device may be designed for operation in the radial flow regulator 32's above nominal "control zone" where the flow rate (Q) is relatively insensitive to changes in the driving pressure difference (P) . This may be highly desirable, since the patient will receive the medication 12 at the needed flow rate (Q) ; despite any variations in the driving pressure difference (P) , such as may be caused by the gradual emptying of the medication delivery device. In addition, if the nominal "control zone" driving pressure difference (P) were to be substantially exceeded, such as if a medical person accidentally overfilled the medication delivery device, then the medication flow rate (Q) will actually fall, thereby significantly reducing the possibility of injury or death to the patient, due to an overdose of medication 12, which might otherwise occur. The radial flow regulator 32 tends to maintain the flow rate (Q) of the medication 12 at a relatively constant value in its "control zone", despite changes in the driving pressure difference (P) , in the following way. If the driving pressure difference (P) increases, then the flexure 28 will tend to be deflected downwardly towards the regulator seat 42 an increased amount, thereby reducing the height of the regulator gap 48. This, in turn, tends to maintain the flow rate (Q) at a relatively constant value, despite the increased driving pressure difference (P) . This is because the reduced height of the regulator gap 48 will tend to compensate for the increased driving pressure difference (P) by reducing the flow rate (Q) which would otherwise occur at that increased driving pressure difference (P) . On the other hand, if the driving pressure difference (P) decreases, then the flexure 28 will tend to be deflected downwardly towards the regulator seat 42 a decreased amount, thereby increasing the height of the regulator gap 48. This, in turn, tends to maintain the flow rate (Q) at a relatively constant value, despite the reduced driving pressure difference (P) . This is because the increased height of the regulator gap 48 will tend to compensate for the reduced driving pressure difference (P) by increasing the flow rate (Q) which would otherwise occur at that reduced driving pressure difference (P) . Lastly, at driving pressure differences (P) above the regulator 32's "control zone", the flow rate (Q) is gradually reduced to near zero, as the flexure 28 is driven down closer and closer to the regulator seat 42. Although the radial flow regulator 32 is deceptively simple in appearance, it has been discovered that it is not possible to develop simple, generally applicable design rules for its construction. This is in large part attributable to the close and nonlinear compensatory coupling between the flow rate (Q) through the radial flow regulator 32's regulator gap 48 and the flow resistance of the regulator gap 48 (R 8 ) ; which, in turn, makes it difficult to separate cause and effect in a mathematical sense. In addition, certain other problems arise in developing simple, generally applicable design rules for the radial flow regulator 32 because the flow rates (Q) of the medication 12 through the regulator 32 may be so low, (as low as about 0.01 cc per day), and because the dimensions of the inlet channels 38, the inlet cavity 40, the regulator gap 48, the outlet cavity 52 and the outlet port 54 may be so small, (as small as about 0.1 microns). As a result of such low flow rates (Q) and such small dimensions, certain fluid flow effects (such as the viscous shear forces of the medication 12 acting to deform various parts of the radial flow regulator 36) , which are normally negligible in predicting the performance of physically larger flow regulators, which handle flow rates of over about 0.1 cc per minute, for example, may become very important. In addition, certain other fluid flow effects (such as the Equation of Continuity and Bernoulli's Equation) , which are normally important for physically larger flow regulators, handling such higher flow rates (Q) , may become negligible for a regulator 32 having such low flow rates (Q) and such small dimensions. And, at intermediate flow rates (Q) and dimensions, a combination of the pertinent small scale and large scale fluid flow effects may have to be taken into account. Because of all of the above problems, it has been discovered that two quite different strategies may be used to assist in designing a radial flow regulator 32 which has any particular desired flow regulation characteristics. The first strategy is one which is empirical in nature. That is, a series of flow regulators 32 may be built, and one feature at a time may be varied, so that the effects of changing that particular feature may be determined. For example, the series flow resistance (R s ) of the regulator gap 48 may be independently varied by holding constant the regulator gap 48's initial height (when the driving pressure difference (P) is equal to zero) ; while varying the width of the ring-shaped regulator seat 42, such as by varying the I.D. and O.D. of the ring-shaped regulator seat 42. Similarly, the regulator gap 48's initial height (when the driving pressure difference (P) is equal to zero) may be varied; while holding constant the width of the ring shaped regulator seat 42, such as by holding constant the I.D. and O.D. of the ring-shaped regulator seat 42. By building and testing a large number of radial flow regulators 32; by then plotting data points for each of them for their various flow rates (Q) versus their driving pressure differences (P) ; and by then curve-fitting the plotted data points, it has been discovered that it is possible to generate an empirical model for the performance of the radial flow regulator 32 which shows the relationships between key features of the radial flow regulator 32 and the operating behavior of the radial flow regulator 32. These empirical relationships may then be used to interpolate or extrapolate from known design cases to predict the behavior of a new radial flow regulator 32. For example, it has been discovered that the radial flow regulator 32's flow rate set point (Q Bβt ) (the average flow rate (Q) of the radial flow regulator 32 over its "control zone") obeys power-law relationships with respect to many of the radial flow regulator 32's design features. That is, it has been discovered that if the series flow resistance (R s ) of the regulator gap 48, and the regulator gap 48's initial height (when the driving pressure difference (P) is equal to zero) , are independently varied, then the radial flow regulator 32's flow rate set point (Q sβt ) may be described over a considerable range of values by an equation of the form: where (Q set ) and (R β ) are as have been defined above; where (G) is the regulator gap 48's initial height (when the driving pressure difference (P) is equal to zero) ; and where (a) is a constant. For example, for a radial flow regulator 32 having a silicon flexure 28 with a thickness of about 25 microns; having channels 38 with a width of about 107 microns, with a depth of about 5.65 microns, and a length of about 2.54 mm; having a ring-shaped inlet cavity 40 with an O.D. of about 2,300 microns, and a depth of about 5.65 microns; having a ring-shaped regulator seat 42 with a width (as measured between its I.D. and O.D.) of about 750 - 2,000 microns; having an initial regulator gap 48 height (when the driving pressure difference (P) is equal to zero) in the range of about 2 - 3 microns; having an outlet cavity 52 about 5.65 microns deep; and having an outlet port 54 with a minimum diameter of about 100 microns and a length of about 494 microns, it has been discovered that (m) is on the order of about 2.4 and (n) is on the order of about 2/3. The second strategy which may be used to assist in designing a radial flow regulator 32 which has any particular desired flow regulation characteristics is to develop a sophisticated physical model using numerical methods. The starting point for formulating the model may be that, for any particular radial flow regulator 32, the flow of the medication 12 through it may be generally governed by the following equation: Q=- (R ch +R S {Q) ) where (Q) , (P) , and (R s ) are as has been defined above; where (R cn ) is the combined flow resistance across the radial inlet channels 38; where (R ch ) is a direct function of the length (L) and the wetted perimeter (C) of each of the radial inlet channels 38; where (R ch ) is an inverse function of the cross-sectional area (A) of each of the radial inlet channels 38; and where (R β ) is a nonlinear function of the flow rate (Q) . That is, the flow rate (Q) is proportional to the driving pressure difference (P) , and is inversely proportional to the sum of the two flow resistances (R ch ) and (R s ) . A circuit diagram illustrating this behavior is shown in Fig. 4. It has been found that accurate prediction of the nonlinear flow resistance (R s ) of the regulator gap 48 may require the consideration of at least the following four factors. First, the nonlinear flow resistance (R s ) of the regulator gap 48 may be a function of the pressure drop across the inlet channels 38, due to their flow resistance (R ch ) . This is because the greater the pressure drop across the inlet channels 38, the greater the driving pressure difference (P) across the flexure 28, and the greater the amount of the deflection of the flexure 28 (and vice versa) . This, in turn, generally decreases the height of the regulator gap 48; thereby generally increasing the flow resistance (R s ) of the regulator gap 48 (and vice versa) . However, such deflection of the flexure 28 is not uniform, since the deflected flexure 28 is not flat, but instead assumes a convex, or bowed shape. This results in the nonlinear flow resistance (R β ) of the regulator gap 48 being a relatively complex function of the flow resistance (R ch ) of the inlet channels 38. Second, the nonlinear flow resistance (R β ) of the regulator gap 48 may be a function of the viscous shear forces of the medication 12 acting on the flexure 28's bottom surface 50 as the medication 12 flows radially inwardly through the regulator gap 40, from the inlet cavity 40 to the outlet cavity 52. Such viscous shear forces are, in turn, a function of such things as the viscosity and velocity of the medication 12 in the regulator gap 48. Such viscous shear forces are directed radially inwardly on the flexure 28's bottom surface 50, and tend to twist or distort the flexure 28's bottom surface 50 with respect to the flexure 28's top surface 62. Such twisting or distorting of the flexure 28 tends to vary the size and shape of the regulator gap 48 which, in turn, varies the flow resistance (R 8 ) of the regulator gap 48. This results in the nonlinear flow resistance (R s ) of the regulator gap 48 being a relatively complex function of the viscous shear forces of the medication 12 acting on the flexure 28. Third, the nonlinear flow resistance (R s ) may be a function of the velocity of the medication 12 passing through the regulator gap 48. Such velocity is, in turn, a function of such factors as the flow resistance (R ch ) of the inlet channels 38; the driving pressure difference (P) across the regulator 32; the height, size and shape of the regulator gap 48; and the flow resistance (R s ) of the regulator gap 48. Because of the Equation of Continuity and Bernoulli's Equation, as the velocity of the medication 12 through the regulator gap 48 increases, the pressure of the medication 12 within the regulator gap 48 tends to decrease (and vice versa) . This is because the Equation of Continuity requires that the velocity of the medication 12 must increase at a restriction. Thus, since the regulator gap 48 is a restriction (as compared to the inlet cavity 40) , the velocity of the medication 12 must increase as it flows through the regulator gap 48. Bernoulli's equation then requires that the pressure of the medication 12 in the regulator gap 48 must fall, due to its increased velocity as it flows through the regulator gap 48. That is, as the velocity of the medication 12 in the regulator gap 48 increases, the pressure of the medication 12 in the regulator gap 48 decreases. This increases the amount of the deflection of the flexure 28; which, in turn, generally decreases the height of the regulator gap 48 and increases the flow resistance (R s ) (and vice versa) . Fourth, the nonlinear flow resistance (R s ) may be a function of the flexure 28's thickness, resiliency, elasticity and stiffness. This is because for any given forces acting on the flexure 28, the amount of the deflection of the flexure 28, and the shape (or radial profile) of the deflected flexure 28, may be a function of the flexure 28's thickness, resiliency, elasticity and stiffness. In the forgoing discussion, it was assumed that the membrane 36's inlet channel cover portions 30 were selected such that they would not be deflected a substantial amount downwardly into the inlet channels 38 by the medication 12 during the operation of the radial flow regulator 32. Thus, the forgoing discussion assumed that substantially none of the regulation of the flow of the medication 12 by the flow regulator 32 was done by any such deflection of the 36's inlet channel cover portions 30. However, this need not be the case since, as will be made apparent by all of the disclosures in this document, regulation of the flow rate (Q) of the medication 12 through the radial flow regulator 32 may be at least partially done by such deflection of the membrane 36's inlet channel cover portions 30. From the forgoing, it is seen that the primary difficulty in developing a sophisticated physical model for the radial flow regulator 32 which uses numerical methods is that the amount of the deflection or bowing of the flexure 28, and the shape of the flexure 28 as it deflects or bows, are closely coupled and nonlinear in interaction. As a result, iterative techniques may be used to generate a solution for the flexure 28's deflected or bowed shape (a) that is correct at every point of contact between the medication 12 and the flexure 28 in terms of the forces applied to the flexure 28; and (b) that simultaneously provides a consistent radial gradient of the driving pressure difference (P) of the medication 12 across the flexure 28 which obeys the laws of fluid flow. To do this, a free body diagram may first be developed for an arbitrary ring-shaped segment of the flexure 28. This model creates the following governing fourth-order differential equation set that identifies the relationship between the flexure 28's local curvature and its thickness; Young's modulus and Poisson's ratio; and exterior forcing functions that include the shear between the medication 12 and the flexure 28, any driving pressure difference (P) across the flexure 28, and the flexure 28's radial tension. The governing fourth-order differential equation set may be determined in the following way. The first derivative of the deflection (β ) of the flexure 28 towards the regulator seat 42 is given by the following second order differential equation: Equation 1 where r is radial position with respect to the center of the flexure 28; ΔP(r) is the driving pressure difference across the flexure 28 at the radial position r; and D t is given by: where E is Young's Modulus; t is the thickness of the flexure 28; and υ is Poisson's ratio. The actual deflection Y{r) of the flexure 28 is obtained by integrating above Equation l: r Equation 2 where Y 0 is the centerline deflection of the flexure 28. Hence the governing differential equation set is fourth order. Next, a first-order differential equation may be developed for the flexure 28's driving pressure difference (P) pressure drop across the annular ring-shaped portion of the regulator gap 48 which is directly under the above mentioned arbitrary ring-shaped segment of the flexure 28. This differential equation must take into account not only the change in the regulator gap 48 caused by the amount of the deflection or bowing of the flexure 28, but also any change in the regulator gap 48 caused by the substrate 34's inlet channels 38 and inlet cavity 40. The first-order differential equation for the driving pressure difference ΔP(r) is: Equation 3 where AP X is the driving pressure difference (P) at the outer rim of the inlet cavity 40, referenced to the constant pressure of the medication 12 external to the flexure 28; Q is the volumetric flow rate of the medication 12; μ is the viscosity of the medication 12; and H(r) is the height of the regulator gap 48 when the driving pressure difference (P) is equal to zero. In short, the above Equation 2 describes the amount and shape of the deflection or bowing of the flexure 28; while the above Equation 3 provides a means to calculate the driving pressure difference (P) of the medication 12 across the flexure 28 at any radial position with respect to the flexure 28. To be a physically correct representation of the interaction between the driving pressure difference (P) across the flexure 28, and the amount and shape of the deflection or bowing of the flexure 28, the solutions of the above Equations 2 and 3 must be consistent with each other in a point-to-point sense across the entire radius of the flexure 28. To achieve this goal, the above Equation 2 may be converted to a finite difference form, and a guess may be made as to the radial profile of the driving pressure difference (P) of the medication 12 across the flexure 28. This is necessary since a solution of the bowing or deflected flexure 28's above Equation 2 requires knowledge of the driving pressure difference (P) of the medication 12 across the flexure 28 at each radial position. This results in a so-called tridiagonal array of coupled equations that may be solved recursively for the flexure 28's radial slope at each point. Then this may be integrated once to yield the flexure 28's deflection at each radial position. Once this is known, the radial profile of the driving pressure difference (P) across the flexure 28 may be recalculated using these new deflection values for the flexure 28 by integration of the above Equation 3. The above iterative process may then be continued, as necessary, until the calculated position of the flexure 28 does not change by some arbitrarily set small amount per iteration, thereby signalling a consistent solution set. Any number of different cylindrically-symmetric fluid flow devices may be modeled with the above equation set. By changing the sign of Q, both inward and outward flow of the medication 12 through the devices may be modeled. By adjusting the function H(r) to reflect the height of the gap between the particular fluid flow device's flexure and the corresponding part of its substrate, the above equation set may be equally useful for modeling flow switches (such as the flow switch 250) , one-way valves (such as the one¬ way valves 210, 240, 300), and other flow regulators (such as the flow regulators 80, 110). In the particular case of one-way valves (such as the one-way valve 300) , in which there is a pre-set interference or prestressing between the seat 310 and the flexure 314, that is, the seat 310 protrudes above the plane of the flexure 314's bottom surface 322, it is only necessary to initiate solution of the coupled equations with a trial deflected shape of the flexure 314 that clears the seat 310 and allows the medication 12 to begin to flow radially inwardly across the seat 310. Fig. 5 shows the above mathematical model being used to predict the response of a typical design for the flow regulator 32. The solid curve 72 in Fig. 5 shows a plot of the above mathematical model for the radial flow regulator 32, in terms of flow of the medication 12 through the regulator 32 in μL/day as a function of the driving pressure difference (P) across the flexure 28. The diamond-shaped data points 74 which are plotted in Fig. 5 are for a typical radial flow regulator 32 having a radial array of four rectangular inlet channels 38, each having a width of about 70 microns, a length of about 1270 microns, and a depth of about 5.7 microns; an inlet cavity having a maximum diameter of about 2290 microns, and a depth of about 5.7 microns; a regulator seat 42 having an I.D. of about 508 microns, and an O.D. of about 1780 microns; a flexure manufactured from a membrane of silicon having a thickness of about 25 microns; a regulator gap 48 having a height of about 2.5 microns (when the driving pressure difference (P) across the flexure 28 is zero) ; an outlet cavity having a diameter of about 508 microns, and a depth of about 5.7 microns; and an outlet port having a minimum diameter of about 100 microns, and a length of about 494 microns. The dashed curve 76 is an empirical curve which is derived by applying curve-fitting techniques to the plotted data points 74. As seen in Fig. 5, agreement between the theoretical curve 72 and the plotted data points 74 is very good. The curve 78 in Fig. 6 shows the above mathematical model being used to predict the reduction in the medication 12's flow rate setpoint (Q set ) caused by sealing off the four inlet channels 38 one-by-one. The diamond-shaped data points 74 which are plotted in Fig. 6 are for a typical radial flow regulator 32 having the physical parameters which were set forth above. As seen in Fig. 6, when one inlet channel 38 is sealed off, the effective combined flow resistance (R cn ) of the remaining three channels 38 increases by about 33%, as compared to the combined flow resistance (R cn ) of the original array of four inlet channels 38. Similarly, plugging two and three of the inlet channels 38 will increase the effective combined flow resistance (R ch ) of the remaining inlet channel(s) 38 by about 100% and about 400%, respectively. As seen in Fig. 6, the mathematical model curve 78 predicts this behavior of the radial flow regulator 32 very well. The qualitative effect of closing off one or more of the inlet channels 38 is to increase the driving pressure difference (P) across the flexure 28 which is needed for any given flow rate (Q) of the medication 12 through the radial flow regulator 32. This causes the flexure 28 to come into closer proximity to the regulator seat 42 at a lower flow rate (Q) , and hence biases the regulator 32's flow rate setpoint (Q set ) to a value for the flow rate (Q) which is lower than would otherwise be the case. It has been discovered that, as seen in Fig. 3, as the number of the inlet channels 38 is decreased, the "control zone" of the flow rate (Q) occurs at lower and lower flow rates (Q) for any given driving pressure difference (P) across the radial flow regulator 32. It has also been discovered that, as is also seen in Fig. 3, as the number of the inlet channels 38 is decreased, there may be a reduced sensitivity in the rate of change of the flow rate (Q) for any given change in the driving pressure difference (P) in the "control zone" of the flow rate (Q) . However, the theoretical grounds for this behavior of the regulator 32 are not clear, and it is possible that this behavior may be due to an artifact in a regulator 32 which is imperfect. All of the forgoing is very important, since it has been discovered that a single radial flow regulator 32 may actually have the properties of four different regulators 32, depending on whether none, one, two or three of its inlet channels 38 are sealed. That is, as seen in Fig. 3, such regulators 32 have quite different regulation curves 64, 66, 68, 70; have quite different "control zones" and flow rate set points (Q set ) , have quite different flow rates (Q) for any given driving pressure difference (P) ; and have quite difference sensitivities to changes in their flow rates (Q) for any given change in the driving pressure difference (P) . This makes the present invention much more versatile, since a single radial flow regulator 32 may be easily modified to do the work of four single-function flow regulators. Of course, as was mentioned above, there may be fewer, or more, than four inlet channels 38; so one radial flow regulator 32 may be easily modified to do the work of fewer or more single-function flow regulators 32. From the disclosures in this document, it is possible to selectively design a radial flow regulator 32 for any particular desired flow regulation characteristics or driving pressure difference (P) . This may be done by selectively adjusting one or more of the pertinent parameters, such as: (a) the number, length, size, and cross sectional configuration of the radial inlet channels 38; (b) the number, size, cross-sectional configuration and location of the cavities 40, 52 and the outlet port 54; (c) the number, size, cross-sectional configuration and height of the regulator seat 42; (d) the number, size, cross- sectional configuration and height of the regulator gap 48; and (e) the thickness, resiliency, elasticity and stiffness of the membrane 36. For example, it has been discovered that by adjusting the fraction of the driving pressure difference (P) that is dropped across the radial inlet channels 38 in relation to the fraction of the driving pressure difference (P) which is dropped across the regulator gap 48 (by adjusting the flow resistance (R ch ) of the inlet channels 38 and the flow resistance (R s ) of the regulator gap 48 with respect to each other) , two things may be selectively modified. First, the degree of control of the regulator flow (Q) versus the driving pressure difference (P) may be selectively varied; and second, the amount of regulator flow (Q) versus the driving pressure difference (P) may also be selectively varied. MICROMACHINED RADIAL FLOW REGULATOR 32 (FIGS. 1 - 6): MANUFACTURE The substrate 34 may be manufactured from any suitable strong, durable material which is compatible with the medication 12, and in which the inlet channels 38, the inlet cavity 40, the regulator seat 42, the outlet cavity 52, and the outlet port 54 may be manufactured in any suitable way, such as by using any suitable etching, molding, stamping and machining process. Such a machining process may include the use of physical tools, such as a drill; the use of electromagnetic energy, such as a laser; and the use of a water jet. The membrane 36 may be manufactured from any suitable strong, durable, flexible, material which is compatible with the medication 12. If the radial flow regulator 32 is intended to regulate a medication 12 which is to be supplied to a human or an animal, then any part of the regulator 32 which is exposed to the medication 12 should be manufactured from, and assembled or bonded with, non-toxic materials. Alternatively, any toxic material which is used to manufacture the regulator 32, and which is exposed to the medication 12 during use of the regulator 32, may be provided with any suitable non-toxic coating which is compatible with the medication 12. Suitable materials for the substrate 34 and the membrane 36 may be metals (such as titanium) , glasses, ceramics, plastics, polymers (such as polyimides) , elements (such as silicon) , various chemical compounds (such as sapphire, and mica) , and various composite materials. The substrate 34 and the membrane 36 may be assembled together in any suitable leak-proof way. Alternatively, the substrate 34 and the membrane 36 may be bonded together in any suitable leak-proof way, such as by anodically bonding them together; such as by fusing them together (as by the use of heat or ultrasonic welding) ; and such as by using any suitable bonding materials, such as adhesive, glue, epoxy, solvents, glass solder, and metal solder. Anodically bonding the substrate 34 and the membrane 36 together may be preferable for at least four reasons. First, anodic bonding is relatively, quick, easy and inexpensive. Second, an anodic bond provides a stable leak-proof bond. Third, since an anodic bond is an interfacial effect, there is no build-up of material at the bond; and the bond has essentially a zero thickness, which desirably creates no essentially no spacing between the substrate 34 and the membrane 36. As a result, an anodic bond does not interfere with the desired height of the regulator gap 32. Fourth, an anodic bond may be preferable since it eliminates the need for any separate bonding materials, which might otherwise clog or reduce the size of the inlet channels 38, the inlet cavity 40, the regulator seat 42, the regulator gap 48, the outlet cavity 52, and the outlet port 54; or which might lead to corrosion of the joint between the regulator 32's substrate 34 and membrane 36. One example of how the radial flow regulator 32 may be manufactured will now be given. The starting point may be a 76.2 mm diameter wafer of Corning 7740 Pyrex glass, which will form the regulator 32's substrate 34. The glass wafer may be cleaned in any suitable way, such as by immersing it in a buffered hydrofluoric acid (BHF) etchant for two minutes, rinsing it with distilled water, and drying it. A thin chrome metallization layer may then applied to the top surface of the glass wafer by any suitable means, such as with an electron beam evaporator. The chrome layer may provide a good adhesion surface for the subsequent application of photosensitive resist (photoresist) to the glass wafer's top surface. Following this, a thin layer of any suitable photoresist may be applied on top of the chrome layer, such as Microposit 1650 photoresist made by the Shipley Company, located in Newton, Massachusetts. The layer of photoresist may be dried in any suitable way, such as by baking it at about 90°C for about 25 minutes. An image of the four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52 may then be exposed onto the photoresist in any suitable manner, such as by using a first mask and a mask aligner. This image may be developed (that is, the exposed photoresist may be removed) , by using any suitable photoresist developer, such as 351 developer, made by the above Shipley Company. The glass wafer may then be then rinsed in distilled water and dried. As a result of the forgoing procedure, the chrome layer will now bear an image, unprotected by the photoresist, of the four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52. The unprotected portions of the chrome layer may then be removed by using any suitable chrome etch solution, such as Cyantek CR-7, made by the Cyantek Company, located in Fremont, California. The forgoing procedure will result in an image of the four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52 having been formed on the top surface of the glass wafer, which image is unprotected by the layers of photoresist and chrome which cover the rest of the glass wafer's top surface. The image may then be etched into the glass wafer's top surface to any desired depth by any suitable means, such as by immersing the glass wafer's top surface in BHF etchant; rinsing the glass wafer in distilled water, and drying it. A suitable depth may be about 6.0 microns. Next, an image of the regulator seat 42 may then be exposed onto the photoresist on the glass wafer's top surface using a second mask. The newly exposed photoresist may then be developed; and the newly exposed portions of the chrome removed. Then the image of the regulator seat may be etched into the top surface of the glass wafer to any desired depth in any suitable manner, in order to define an elevation difference between the regulator seat 42's top surface 44 and the top surface of the glass wafer. A suitable elevation difference may be about 2.5 microns. At this point, it may be noted that the depths of the four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52 will also have been automatically increased by about 2.5 microns, since they are also unprotected by the layers of chrome and photoresist. In other words, the four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52 may intentionally be initially etched to a depth less than their desired final depth, in order to permit them to automatically and simultaneously reach their desired final depth while the regulator seat 42 was being etched. Note that the above procedure is unusually economical and quick, since if the four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52 were originally etched to their desired final depth, then the additional steps of re-coating the entire glass wafer with photoresist (in order to protect the etched four radial inlet channels 38, the inlet cavity 40, and the outlet cavity 52), and then baking the photoresist, would have to be done prior to the exposing, developing and etching of the regulator seat 42. After the regulator seat 42 has been etched, the regulator 32's outlet port 54 may be formed by any suitable means, such as by drilling it with a focused beam from a 25W C0 2 laser, with a physical drill, or with a water jet drill. It has been discovered that when using a laser to form the outlet port 54, heating the glass wafer to near its anneal point improves the quality of the outlet port 54, and also reduces undesirable cracking of the glass wafer adjacent to the outlet port 54. Preferably, as seen in Fig. 2, the outlet port 54 may have a venturi-like shape, rather than being cylindrical in shape, for better fluid flow through it. It has also discovered that the outlet port 54 may be given its preferred venturi-like shape by drilling the outlet port 54 with a laser in the manner discussed above. The desired venturi-like shape may be automatically formed during the laser drilling process, and apparently results from the thermal effects of the laser beam interacting with the glass wafer as the outlet port 54 is being drilled through it with the laser beam. After the outlet port 54 has been drilled, the glass wafer may be lightly etched with BHF etchant, in order to remove any volatilized glass which may have condensed on the glass wafer adjacent to its outlet port 54. After the outlet port 54 has been formed, a nominal layer of one or more corrosion-resistant substances may be deposited onto the top surface of the glass wafer by any suitable means, such as by sputtering using an e-beam evaporator. As a result, the four radial inlet channels 38, the inlet cavity 40, the regulator seat 42, the outlet cavity 52, and the outlet port 54 will have been coated with a layer of the corrosion-resistant substance(s) . Suitable corrosion-resistant substances may be silicon, or may be metals, such as gold, platinum, chrome, titanium and zirconium, or may be the oxides of silicon or such metals. Such oxides may be formed by thermally oxidizing the corrosion-resistant substance(s) in air after it has been applied to the substrate 34. However, other suitable corrosion-resistant substances may be used. depending on the particular medication 12 with which the radial flow regulator 32 is designed to be used. The oxides of metals such as titanium and zirconium are well- known to be stable against water solutions over a wide pH range. The thickness of the layer of the corrosion- resistant substance(s) may be from 200 A - 1000 A; but the thickness may depend on the particular corrosion-resistant substance(s) being used, and on the particular medication 12 with which the radial flow regulator 32 is designed to be used. Alternatively, the layer of corrosion-resistant substance(S) may comprise a donut-shaped disk of such corrosion-resistant substance(s) , such as silicon, which may be bonded to the regulator seat 42's top surface 44 by any suitable means, such as by using any of the means which have been mentioned for bonding the substrate 34 and the membrane 36 together. Such a corrosion-resistant donut-shaped disk may be formed in any suitable way, such as by using a masking and etching process which is similar to that described above regarding the substrate 34. The starting point may be a clean epitaxial-coated silicon wafer, to which is applied a thin chrome metallization layer and a layer of photoresist. After the photoresist is dry, an image of the donut-shaped disk may then be exposed onto the photoresist. The exposed photoresist, and the underlying portions of the chrome layer, may then be removed, resulting in an image of the donut-shaped disk on the surface of the silicon wafer, which image is not protected by the photoresist or by the chrome layer. The exposed portions of the silicon wafer may then etched to a depth in excess of the desired thickness of the desired donut-shaped disk in any suitable way, such as by the use of an isotropic silicon etchant. For example, if a donut-shaped disk having a thickness of about 1 micron was desired, then the exposed portions of the silicon wafer may be etched to a depth of about 5 microns. The silicon wafer may then be cleaned; the etched faces of the silicon and glass wafers may then be aligned with each other, so that the donut-shaped disk on the silicon wafer is aligned with the regulator seat 42 on the glass wafer; and the silicon and glass wafers may then be bonded together in any suitable way, such as by using an anodic bonding process like that which will be described below regarding anodically bonding together the silicon and glass wafers that will form the regulator 32's substrate 34 and membrane 36. Next, the silicon wafer with the donut- shaped disk may then etched again in any suitable way, such as by the use of an anisotropic ethylene diamine etchant, until the desired ultimate thickness of the donut-shaped disk of silicon is obtained. The manufacture of only one substrate 34 and only one donut-shaped disk of corrosion-resistant material for the substrate 34's regulator seat 42 was described above. However, it will be appreciated that on any pair of glass and silicon wafers respective arrays of substrates 34 and corresponding donut-shaped disks of corrosion-resistant material may be manufactured simultaneously in a manner which is similar to that described above. If such is the case, the array of substrates 34 on the glass wafer may be aligned with, and then bonded to, the corresponding array of donut-shaped disks of corrosion-resistant material on the silicon wafer. After the final etching of the silicon wafer, the manufacture of each regulator 32 may then be completed in the manner which is set forth below. If a donut-shaped disk or layer of corrosion-resistant substance(s) is bonded or applied to the regulator seat 42, then the regulator seat 42 may have to be etched an additional amount during its above etching step prior to applying the donut-shaped disk or layer of corrosion- resistant substance(s) to the regulator seat 42's top surface 44. The additional amount of etching may be equal to the thickness of the donut-shaped disk or layer, in order to end up with the desired elevation difference between the regulator seat 42's top surface 44 and the top surface of the glass wafer (which will form the substrate 34) . It has been discovered that the donut-shaped disk or layer of corrosion-resistant substance(s) on the regulator seat 42's top surface 44 may serve an unexpected further function in addition to its corrosion-resistant function. That is, it may also prevent the regulator 32's membrane 36 from being inadvertently bonded to the regulator seat 42's top surface 44 when the membrane 36 is being bonded to the glass wafer, such as when the membrane 36 is being anodically bonded in the manner which will be described below. After the regulator seat 42 has been etched, and after any desired layer or disk of corrosion-resistant substance(s) has been applied to etched portions of the glass wafer, the photoresist and chrome which remain on the unetched portions of the glass wafer may be removed by any suitable means, such as by using standard lift-off techniques. Fabricating the membrane 36 and mounting it to the glass wafer (which is the substrate 34) , may be done in any suitable way. One suitable way is to start with a prime silicon wafer having a boron-doped epitaxial silicon layer which has been deposited onto its top surface. Since the boron doped epitaxial silicon layer will ultimately form the regulator 3 's membrane 36, the layer's thickness will depend on the desired thickness of the membrane 36. The boron-doped epitaxial silicon layer, and thus the membrane 36, may be from 1 - 50 microns thick, for example. The boron doping may be in excess of 3 X 10 19 atoms of boron per cubic centimeter, which conveys a dramatic etch- resistance to the epitaxial silicon layer in silicon etchants based on ethylene diamine. The glass and silicon wafers may then be cleaned; dried; and anodically bonded together. The anodic bonding may be performed in any suitable way, such as by placing the respective top surfaces of the glass and silicon wafers in contact with each other in a vacuum chamber in an oven maintained at a temperature of about 500°C. A DC voltage of approximately 1000 volts may then be applied to the two wafers for a period of about 15 minutes, with the silicon wafer at a positive potential relative to the bottom surface of the glass wafer. An exponentially decaying current will flow through the wafers over this time period, at the end of which the two wafers will have been anodically bonded together, i.e., they will have been hermetically bonded to each other to form a silicon/glass sandwich. It has also been discovered that the anodic bonding process may also ensure that any corrosion- resistant substance(s) which were applied to the etched surfaces of the glass wafer are firmly attached to it. Upon cool-down, after the anodic bonding process is complete, the silicon wafer portion of the anodically bonded silicon/glass sandwich may be ground down; but preferably, the silicon wafer is not ground down so much that any of its boron doped epitaxial silicon layer is removed. For example, if the boron doped epitaxial silicon layer is from about 1 - 50 microns in thickness, then the silicon wafer portion of the bonded silicon/glass wafer sandwich may be ground down to about 125 microns in thickness. The remaining non-doped silicon in the silicon wafer may then be removed in any suitable way, such as by placing the ground down silicon/glass sandwich in an ethylene diamine etchant maintained at 112°C for 3.5 to 4.0 hours. A suitable ethylene diamine etchant may be PSE-300, manufactured by the Transene Corp. located in Rowley, Massachusetts. At the end of this time, the boron doped epitaxial silicon layer will be exposed in the form of a continuous, flat membrane 36 which is anodically bonded to the glass wafer (the substrate 34) , thereby forming the completed radial flow regulator 32, which is then cleaned and dried. The purpose of the above grinding step is simply to reduce the amount of silicon which needs to be etched away. Accordingly, as alternatives, the grinding step may be eliminated, with all of the undesired silicon being etched away; or a thinner silicon wafer may be used, so that there is less undesired silicon to begin with. The manufacture of only one radial flow regulator 32 was described above. However, it will be appreciated that on any pair of glass and silicon wafers numerous regulators 32 could be manufactured simultaneously in a manner similar to that described above. If such is the case, an array of substrates 34 may be simultaneously etched in the glass wafer before the silicon and glass wafers are aligned and bonded together. Then, all of the membranes 36 may be formed simultaneously by grinding and etching the silicon wafer to its desired final thickness. The silicon/glass sandwich may then be divided by any suitable means (such as dicing) into individual chips, each chip bearing at least one radial flow regulator 32. One of the advantages of using the etching and anodic bonding process which was described in detail above is that such a process enables high quality, very reliable radial flow regulators 32 to be mass produced in great numbers at a cost so low that the regulator 32 may be considered to be disposable. In addition, it should also be noted that the regulator 32 is stunning in its simplicity since it may have as few as only two parts (the substrate 34 and the membrane 36) ; and since it may have only one moving part (the membrane 36's flexure 28). Further, because the raw materials from which the regulator 32 may be manufactured may be very inexpensive, such as glass and silicon, the cost of the regulator 32 may held to a very low level. MICROMACHINED LINEAR FLOW REGULATOR 80 HAVING A CONTOURED REGULATOR SEAT 90 (FIGS. 7 - 11): MANUFACTURE The substrate 82 may be made from any suitable strong, durable material which is compatible with the medication 12, and in which the channel 86 and the outlet port 54 may be manufactured in any suitable way, such as by using any suitable etching, molding, stamping and machining process. Such a machining process may include the use of physical tools, such as a drill; the use of electromagnetic energy, such as a laser; and the use of a water jet. The membrane 84 may be made from any suitable strong, durable, flexible, material which is compatible with the medication 12. The membrane 84 may also be elastic. If the regulator 80 is intended to regulate a medication 12 which is to be supplied to a human or an animal, then any part of the regulator 80 which is exposed to the medication 12 should be made from, and assembled or bonded with, non-toxic materials. Alternatively, any toxic material which is used to manufacture the regulator 80, and which is exposed to the medication 12 during use of the regulator 80, may be provided with any suitable non-toxic coating which is compatible with the medication 12. Suitable materials for the substrate 82 and the membrane 84 may be metals (such as titanium) , glasses, ceramics, plastics, polymers (such as polyimides) , elements (such as silicon) , various chemical compounds (such as sapphire, and mica) , and various composite materials. The substrate 82 and the membrane 84 may be assembled together in any suitable leak-proof way. Alternatively, the substrate 82 and the membrane 84 may be bonded together in any suitable leak-proof way, such as by anodically bonding them together; such as by fusing them together (as by the use of heat or ultrasonic welding) ; and such as by using any suitable bonding materials, such as adhesive, glue, epoxy, glass solder, and metal solder. Anodically bonding the substrate 82 to the membrane 84 may be preferable for at least four reasons. First, anodic bonding is relatively, quick, easy and inexpensive. Second, an anodic bond provides a stable, leak-proof bond. Third, since an anodic bond is an interfacial effect, there is no build-up of material at the bond; and the bond has essentially a zero thickness, which desirably creates no essentially no spacing between the substrate 82. and the membrane 84. As a result, an anodic bond does not interfere with the desired height or shape of the regulator gap 99. Fourth, an anodic bond may be preferable since it eliminates the need for any separate bonding materials, which might otherwise clog or reduce the size of the inlet port 88, the channel 86, the regulator gap 99, and the outlet port 92; or which might lead to corrosion of the joint between the substrate 82 and the membrane 84. One example of how the linear flow regulator 80 may be manufactured will now be given. The starting point may be a 76.2 mm diameter wafer of Corning 7740 Pyrex glass, which will form the regulator 80's substrate 82. The channel 86 and its regulator seat 90 may then be formed in the substrate 82 in any suitable way. One suitable way may be to first etch a generally rectangular channel into the substrate 82, wherein the rectangular channel has a length and a depth about equal to the length and the depth of the desired channel 86 and regulator seat 90. The rectangular channel may be etched into the substrate 82 in any suitable way, such as by using a process which is the same as, or at least similar to, that used to etch the radial flow regulator 32's inlet channels 38 into its substrate 34. After the rectangular channel has been etched, the regulator 80's outlet port 92 may be formed. The structure, operation, theory and manufacture of the linear flow regulator 80's outlet port 92 is the same as, or at least similar to, that of the radial flow regulator 32's outlet port 54, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. After the outlet port 92 has been formed, a nominal layer of one or more corrosion-resistant substances may be deposited onto the top surface of the glass wafer in any suitable way. As a result, the channel 86, the regulator seat 90, and the outlet port 92 will have been coated with a layer of the corrosion-resistant substance(s) . The structure, operation, theory and manufacture of such a layer of one or more corrosion-resistant substances for the linear flow regulator 80 is the same as, or at least similar to, that of the radial flow regulator 32's layer of one or more corrosion-resistant substances, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. After the channel 86 and the regulator seat 90 have been etched, and after any desired layer of corrosion- resistant substance(s) has been applied to etched portions of the glass wafer, the photoresist and chrome which remain on the unetched portions of the glass wafer may be removed by any suitable means, such as by using standard lift-off techniques. At this point, certain work on the manufacture of the membrane 84 may be done before the desired channel 86 and regulator seat 90 may be completed. Manufacturing the membrane 84 and bonding it to the glass wafer (which is the substrate 82) may be done in any suitable way. The structure, operation, theory and manufacture of the linear flow regulator 80's membrane 84 and the bonding of the membrane 84 to its substrate 82 to form a silicon/glass sandwich is the same as, or at least similar to, the manufacture of the radial flow regulator 32*s membrane 36, and the bonding of the membrane 36 to its substrate 34 to form a silicon/glass sandwich, except for those differences, which will be made apparent by an examination of all of the Figures and disclosures in this document. Some of those differences will now be addressed. It may be recalled that the starting point for the regulator 80's membrane 84 may be a prime silicon wafer having a boron-doped epitaxial silicon layer which has been deposited onto one of its surfaces. Since the boron doped layer will ultimately form the regulator 80's membrane 84, the boron-doped layer's thickness will depend on the desired thickness of the membrane 84. The boron-doped layer has a dramatic etch-resistance to silicon etchants based on ethylene diamine; but is easily etched by isotropic etchants. The isotropic etchants will also easily etch the non-doped layer of the silicon wafer. Accordingly, the first step in manufacturing the regulator 80's membrane 84 is to first clean the silicon wafer; apply a thin chrome metallization layer to both of the wafer's surfaces; and then apply and dry a thin layer of any suitable photoresist on top of the chrome layer. An image of the inlet port 88 may then be exposed onto the photoresist on the silicon wafer's boron-doped layer. and then developed; after which the silicon wafer may be cleaned and dried. As a result of the forgoing procedure, the chrome layer over the boron-doped layer will now bear an image, unprotected by the photoresist, of the inlet port 88. The unprotected portion of the chrome layer may then be etched away; resulting in an image of the inlet port 88 having been formed on the boron-doped layer, which image is unprotected by the layers of photoresist and chrome which cover the rest of the silicon wafer. The image of the inlet port 88 may then be etched into the boron-doped layer to a depth which is at least slightly greater than the thickness of boron-doped layer in any suitable way, such as by using an isotropic etchant. The photoresist and the chrome layers may then be removed from the silicon wafer, which may then be cleaned and dried. The silicon and glass wafers may then be aligned, so that the etched image of the inlet port 88 in the boron- doped layer is in proper registry with the etched image of the channel 86 in the glass wafer. The etched surfaces of the silicon and glass wafers may then be anodically bonded together; after which the non-doped layer of the silicon wafer may then be etched and ground to produce the desired membrane 84, with the desired inlet port 88. The desired inlet port 88 is automatically formed during the etching and grinding of the non-doped layer of the silicon wafer because the isotropic etchant had previously completely etched away the image of the inlet port 88 in the boron- doped layer of the silicon wafer; so that when the non- doped layer of the silicon wafer is etched and ground away, the inlet port 88 is automatically formed. The desired contour may be imparted to the channel 86's regulator seat 90 in any suitable way. One suitable way may be to use a pressure forming method, in which the substrate 82 may first be placed into a forming device which restrains the substrate 82*s bottom surface 104 and its lateral edges. A flat stencil having a cutout whose length and width corresponds to that of the desired channel 86 may be provided; the membrane 84 may be tightly sandwiched between the stencil and the substrate 82; and at least the substrate 82 may be heated to an elevated process temperature at which the substrate 82 is softened. For example, the elevated process temperature for a Pyrex glass substrate may be about 600°C. The portion of the membrane 84 which is exposed through the stencil (i.e., the flexure 98), may then exposed to a pressure about equal to the regulator 80's maximum designed driving pressure difference (P) , thereby deflecting the flexure 98 down into the softened substrate 82 and forming the channel 86's contoured regulator seat 90. For example, for a Pyrex glass substrate which is heated to about 600°C, the pressure may be about 100 pounds per square inch (psi) . The rectangular channel mentioned above, which was etched into the substrate 82, may aid in the formation of the desired contoured regulator seat 90 since all the deflected flexure 98 needs to do is to mold the rectangular channel's sides and bottom into the desired contour. The forming device for the substrate 82 may have a relief hole which permits the exit of any excess substrate 82 material which is displaced by the deflected membrane 84. Alternatively, the rectangular channel mentioned above may be dispensed with, and the flexure 98 may be deflected with pressure down into the softened substrate 82 to form the contoured regulator seat 90. The desired pressure may then be maintained on the flexure 98 while the substrate 82 is cooled and hardened, thereby forming the substrate 82's channel 86 with the desired contour in its regulator seat 90. The pressure may then be released, allowing the elastic flexure 98 to return to its undeflected configuration. The stencil, the forming device and any undesired displaced substrate 82 material may then be removed. Although the use of a heat softened substrate 82 was described above, the contoured regulator seat 90 may be pressure formed into the substrate 82 in any other suitable way. For example, the substrate 82 may be selected to be made from a material, such as an epoxy, a ceramic material or a solvent-softened material, which is soft at room temperature, and which is then hardened after the flexure 98 is deflected down into it by a chemical reaction, by the application of heat, or by the evaporation of the solvent, respectively. Another way to form the contoured regulator seat 90 may be to micromachine the desired contour into the substrate 82 by use of a laser beam. Such a laser beam may be regulated, by any suitable means, to have an intensity gradient similar to that of the desired contour of the channel 86's regulator seat 90, such as by projecting the laser beam through one or more suitable lenses and/or gradient filters. Another way of using a laser beam to micromachine the desired contour into the substrate 82 may be to project the laser beam through a mask to give at least a portion of the laser beam a cross-sectional configuration which is similar to that the desired contour of the regulator seat 90. The manufacture of only one linear flow regulator 80 was described above. However, it will be appreciated that on any pair of glass and silicon wafers numerous regulators 80 could be manufactured simultaneously in a manner similar to that described above. If such is the case, an array of substrates 82 may be simultaneously etched in the glass wafer before the silicon and glass wafers are aligned and bonded together. Then, all of the membranes 36, and their inlet ports 88 may be formed simultaneously. The silicon/glass sandwich may then be divided by any suitable means (such as dicing) into individual chips, each chip bearing at least one linear flow regulator 80. One of the advantages of using the etching, anodic bonding, and pressure forming process which was described in detail above is that such a process enables high quality, very reliable linear flow regulators 80 to be mass produced in great numbers at a cost so low that the regulator 80 may be considered to be disposable. In addition, it should also be noted that the regulator 80 is stunning in its simplicity since it may have as few as only two parts (the substrate 82 and the membrane 84) ; and since it may have only one moving part (the membrane 84's flexure 98) . Further, the cost of the regulator 80 may held to a very low level because the raw materials from which the regulator 80 may be made may be very inexpensive, such as glass and silicon. MICROMACHINED ONE-WAY MEMBRANE VALVE 210 HAVING A RECTANGULAR FLEXURE AND A RING-SHAPED INLET VALVE SEAT (FIGS. 12 - 14): MANUFACTURE The one-way membrane valve 210's substrate 212 may be manufactured from any suitable strong, durable material which is compatible with the medication 12, and in which the inlet port 216, the inlet cavity 218 and the outlet cavity 224 may be manufactured in any suitable way, such as by using any suitable etching, molding, stamping and machining process. Such a machining process may include the use of physical tools, such as a drill or saw; the use of electromagnetic energy, such as a laser; and the use of a water jet. The membrane 214 may be manufactured from any suitable strong, durable, flexible, material which is compatible with the medication 12, and in which the outlet ports 230 may be manufactured in any suitable way, such as by using any suitable etching, molding, stamping and machining process. Such a machining process may include the use of physical tools, such as a drill or saw; the use of electromagnetic energy, such as a laser; and the use of a water jet. If the one-way membrane valve 210 is intended to be used with a medication 12 which is to be supplied to a human or an animal, then any part of the one-way membrane valve 210 which is exposed to the medication 12 should be manufactured from, and assembled or bonded with, non-toxic materials. Alternatively, any toxic material which is used to manufacture the one-way membrane valve 210, and which is exposed to the medication 12 during use of the one-way valve 210 may be provided with any suitable non-toxic coating which is compatible with the medication 12. Suitable materials for the substrate 212 and the membrane 214 may be metals (such as titanium) , glasses, ceramics, plastics, polymers (such as polyimides) , elements (such as silicon) , various chemical compounds (such as sapphire, and mica) , and various composite materials. The substrate 212 and the membrane 214 may be assembled together in any suitable leak-proof way. Alternatively, the substrate 212 and the membrane 214 may be bonded together in any suitable leak-proof way, such as by anodically bonding them together; such as by fusing them together (as by the use of heat or ultrasonic welding) ; and such as by using any suitable bonding materials, such as adhesive, glue, epoxy, solvents, glass solder, and metal solder. Anodically bonding the substrate 212 and the membrane 214 together may be preferable for reasons which are the same as, or at least similar to, the reasons set forth above for anodically bonding the radial flow regulator 32's substrate 34 and membrane 36 together. It has also been discovered that anodically bonding the substrate 212 and membrane 214 together may be desirable for at least two additional reasons. First, it has been discovered that the elevated temperatures which are used during the anodic bonding process may be used to automatically prestress the flexure 228. This will be discussed in more detail below. Second, it has also been discovered that the elevated temperatures and voltages used during the anodic bonding process may be used to automatically cause the inlet valve seat 220 and the flexure 228 to conform to each other, thereby resulting in a better seal therebetween than might otherwise be the case. This is because such elevated temperatures during the anodic bonding process tend to soften the substrate 212, while such elevated voltages during the anodic bonding process tend to draw the softened substrate 212 and flexure 214 tightly together, thereby physically deforming the flexure 228 and the inlet valve seat 220 enough to "smooth out" to some degree any microscopic irregularities which may be present on the mating surfaces of the flexure 228 and the inlet valve seat 220. One example of how the one-way membrane valve 210 may be manufactured will now be given. The starting point may be a 76.2 mm diameter wafer of Corning 7740 Pyrex glass, which will form the one-way membrane valve 210's substrate 212. The inlet cavity 218 and the outlet cavity 224 may be manufactured in the substrate 212 in any suitable way. One suitable way may be to use an etching process which is the same as, or at least similar to, that used to form the radial flow regulator 32's inlet channels 38, inlet cavity 40, regulator seat 42 and outlet port 54 of Figs. 1 - 2, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. The inlet port 216 may then be formed in the substrate 212 in any suitable way. The structure, operation, theory and manufacture of the one-way membrane valve 210's inlet port 216 may be the same as, or at least similar to, those of the radial flow regulator 32's outlet port 54 of Figs. 1 - 2, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. Next, a nominal layer of one or more corrosion- resistant material substances may then be deposited onto all of the surfaces of the inlet port 216, the inlet cavity 218, the inlet valve seat 220, and the outlet cavity 224. The structure, operation, theory and manufacture of such a layer of one or more corrosion-resistant substances for the one-way membrane valve 210 may be the same as, or at least similar to, those of the layer of one or more corrosion- resistant substances for the radial flow regulator 32 of Figs. 1 - 2, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. It has been discovered that such a layer of corrosion- resistant substance(s) may serve at least one important function, in addition to its corrosion-resistant function, if the membrane 214 is anodically bonded to the substrate 212. That is, the layer of corrosion-resistant substance(s) may prevent the flexure 228 from being bonded to the inlet valve seat 220 during the anodic bonding process. The membrane 214, with its outlet ports 230, may be manufactured from a silicon wafer, and secured to the glass wafer (which is the substrate 212) in any suitable way. The structure, operation, theory and manufacture of the one-way membrane valve 210's membrane 214, with its outlet ports 230, and the securing of the membrane 214 to its substrate 212 is the same as, or at least similar to, the manufacturing of the linear flow regulator 80's membrane 84, with its inlet port 88, and the securing of its membrane 84 to its substrate 86, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. If it is desired to intentionally prestress the flexure 228, the flexure 228 may be prestressed in any suitable way. One suitable way may be to select materials for the substrate 212 and the membrane 214 which have different thermal expansion coefficients, such as a wafer of 7740 Pyrex glass for the substrate 212 and a wafer of silicon for the membrane 214, for example. Then, after the glass wafer (the substrate 212) has been etched, and the boron-doped layer of the silicon wafer has been etched, the glass and silicon wafers may be heated (or cooled) to a temperature which is higher than (or lower than) the designed operating temperature range of the one-way membrane valve 210. The glass and silicon wafers may then be secured together at that higher (or lower) temperature, in any suitable way. Then, when the one-way membrane valve 210 is returned to its designed operating temperature range, and the manufacture of the membrane 214, with its outlet ports 230, has been completed, the difference in the thermal expansion coefficients of the substrate 212 and the membrane 214 will cause the flexure 228 to be prestressed to the desired amount. For example, if, as mentioned above, the substrate 212 and the membrane 214 were selected to be manufactured from 7740 Pyrex glass and silicon, respectively; and the substrate 212 and the membrane 214 may be bonded together by using anodic bonding at a temperature higher than the one-way membrane valve 210's designed operating temperature range, such as from about 300°C to about 520°C. The manufacture of only one one-way membrane valve 210 was described above. However, it will be appreciated that on any pair of glass and silicon wafers the substrates 212 and the membranes 214 for a large number of one-way membrane valves 210 could be manufactured simultaneously in a manner similar to that described above. If such is the case, an array of substrates 212 may be simultaneously etched in the glass wafer; their inlet ports 216 may be drilled, and the layer of one or more corrosion-resistant substances may be applied to the substrates 212. Then an array of outlet ports 230 may be simultaneously etched in the silicon wafer. Next, the silicon and glass wafers for the substrates 212 and the membranes 214 may be aligned and bonded together. Then, all of the membranes 214 may be formed simultaneously by grinding and etching the silicon wafer to its desired final thickness. The silicon/glass substrate 212/membrane 214 sandwich may then be divided by any suitable means (such as dicing) into individual chips, each chip bearing at least one one-way membrane valve 210. One of the advantages of using etching and anodic bonding processes to manufacture the one-way membrane valve 210, is that such processes enable high quality, very reliable, one-way membrane valves 210 to be mass produced in great numbers at a cost so low that the one-way membrane valves 210 may be considered to be disposable. Other advantages of using an anodic bonding process to bond the substrate 212 and the membrane 214 together were described in detail above, i.e., to prestress the flexure 228, and to conform the inlet valve seat 220 and the flexure 228 to each other, for a better seal therebetween. Further, it should also be noted that the one-way membrane valve 210 is stunning in its simplicity since it has only two basic parts, i.e. its substrate 212 and its membrane 214; and since only one of its parts is a moving part, i.e., its flexure 228, which merely bows during operation of the one-way membrane valve 210. Further, because the raw materials from which the one-way membrane valve 210 may be manufactured may be very inexpensive, such as glass and silicon, the cost of the one-way membrane valve 210 may held to a very low level. MICROMACHINED ONE-WAY MEMBRANE VALVE 240 HAVING A RECTANGULAR FLEXURE AND A RECTANGULAR INLET VALVE SEAT (FIGS. 15 - 18) : MANUFACTURE The micromachined one-way membrane valve 240 which is illustrated in Figs. 15 - 17 is the same as, or at least similar to, the micromachined one-way membrane valve 210 of Figs. 12 - 14 in its manufacture, except for those differences which will be made apparent by an examination of all of the Figures and all of the disclosures in this document. The inlet port 216 and the inlet cavity 218 may be manufactured in the substrate 212 in any suitable way. One suitable way may be simultaneously etch them into the substrate 212 by using an etching process which is the same as, or at least similar to, that used to form the radial flow regulator 32's inlet channels 38, inlet cavity 40, regulator seat 42 and outlet port 54 of Figs. 1 - 2, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. MICROMACHINED ONE-WAY MEMBRANE VALVE 300 HAVING A CIRCULAR FLEXURE AND A CIRCULAR INLET VALVE SEAT (FIGS. 19 - 20): MANUFACTURE The micromachined one-way membrane valve 300 which is illustrated in Figs. 19 - 20 is the same as, or at least similar to, the micromachined one-way membrane valves 210, 240 of Figs. 12 - 18 in its manufacture, except for those differences which will be made apparent by an examination of all of the Figures and all of the disclosures in this document. Among those differences are that the desired height difference between the top surfaces 318, 320 of the inlet valve seat 310 and the substrate 302, respectively, may be obtained in any suitable way. One suitable way may be, before the membrane 304 is manufactured and secured to the substrate 302, to etch all of the substrate 302's top surface 320 (except for the inlet cavity 308 and the inlet valve seat 310) , by an amount which is equal to the desired height difference. This etching step may be done in any suitable way, such as by using etching processes which is the same as, or at least similar to, that used to form the radial flow regulator 32's inlet channels 38, inlet cavity 40, regulator seat 42 and outlet port 54 of Figs. 1 - 2, except for those differences, if any, which will be made apparent by an examination of all of the Figures and disclosures in this document. Alternatively, the desired height difference may be obtained by depositing or securing, in any suitable way, a layer of any suitable material of the desired thickness on only the inlet valve seat 310's top surface 318. MICROMACHINED MEMBRANE FLOW SWITCH 250 (FIGS. 21 - 26): STRUCTURE The micromachined membrane flow switch 250 of the present invention is illustrated in Figs. 21 - 26. The flow switch 250 may comprise a substrate 252 and a membrane 254. The substrate 252 may have an inlet switch seat 256, an outlet cavity 258 and a pair of outlet ports 260. Although the substrate 252 is illustrated as being square, it may have any other suitable size and shape. Although the inlet switch seat 256 is illustrated as being cylindrical, and as having a flat top surface 270, it may have any other suitable size and shape; and its top surface 270 may not be flat. Although a single, cylindrical, ring-shaped outlet cavity 258 is illustrated, there could be more than one outlet cavity 258, and each outlet cavity 258 could have any other suitable size and shape. Although a pair of outlet ports 260, each having a venturi-shaped geometric configuration, for better fluid flow therethrough, are illustrated; there may be fewer or more outlet ports 260, and each outlet port 260 may have any other suitable size and shape. The flow switch 250's membrane 254 may have a mounting portion 262, which may be secured to the substrate 252; a flexure 264, which extends over the outlet cavity and part of the inlet switch seat 256; and an inlet port 266, which lies over the inlet switch seat 256. Although the flexure 264 is illustrated as being ring shaped, and as having a uniform thickness, it may have any other suitable size and shape, and its thickness may not be uniform. Although one, circular inlet port 266 is illustrated, there may be more than one inlet port 266, and each inlet port 266 may have any other suitable size and shape. A switch gap 268 may be defined between the inlet switch seat 256 and the flexure 264 when there is a zero driving pressure difference (P) of the medication 12 across the flow switch 250, which is the driving pressure difference (P) between the flexure 264's top surface 265 and the outlet ports 260. By way of example, the flow switch 250 may have the following physical parameters. The substrate 252 may be made from 7740 Pyrex glass, may be a square having sides about 5.0 mm long, and may have a maximum thickness of about 0.5 mm. The outlet cavity 258 may have an inner diameter of about 2.0 mm, an outer diameter of about 3.8 mm, and a depth of about 25 microns as measured from the substrate 252's top surface 278. The outlet ports 260 may have a minimum diameter of about 100 microns, and a length of about 475 microns. The inlet switch seat 256 may have a diameter of about 2.0 mm, and a height above the outlet cavity 258's bottom surface 280 of about 21 microns. The switch gap 268 may be about 4 microns high, when there is a zero driving pressure difference (P) of the medication 12 across the flow switch 250. The membrane 254 may be made from epitaxial silicon, may have a thickness of about 25 microns, and may be a square having sides about 5.0 mm long. The flexure 264 may have an inner diameter of about 250 microns, and an outer diameter of about 3.8 mm. The inlet port 266 may have a diameter of about 250 microns. The flow characteristics of this example flow switch 250 are illustrated in the graphs of Figs. 23 - 26. MICROMACHINED MEMBRANE FLOW SWITCH 250 (FIGS. 21 - 26): OPERATION AND THEORY The flow switch 250 may be installed in its intended location of use in any suitable way. Any suitable medication supply means may be used to connect the flexure 264's top surface 265 and the inlet port 266 to a source of the medication 12; and any suitable medication delivery means may be used to connect the flow switch 250's outlet ports 260 to whatever person, object or thing is to receive the medication 12 from the outlet ports 260. For example, the flow switch 250 may be installed within any type of reservoir means for the medication 12 by any suitable means, such as by locating the flow switch 250's outlet ports 260 over the reservoir means's outlet, and by using an adhesive face seal between the flow switch 250's bottom surface 282 and the inside of the reservoir means to hold the flow switch 250 in place. As a result, when the reservoir means is filled with the medication 12, the flow switch 250 may be immersed in the medication 12, with its inlet channel 266 and its flexure 264's top surface 265 in fluid communication with the medication 12 within the reservoir means, and with its outlet ports 260 in fluid communication with the reservoir means' outlet. Such an installation for the flow switch 250 may have numerous advantages. For example, it is quick, easy, reliable and inexpensive, because no additional medication supply means (such as supply conduits) are needed to supply the medication 12 to the inlet port 266 and the flexure 264's top surface 265 (since they are already immersed in the medication 12); and because no additional medication delivery means (such as delivery conduits) are needed to convey the medication 12 away from flow switch 250's outlet ports 260, (since the reservoir means' outlet is used for this purpose) . Such additional inlet and outlet conduits may be undesirable since it may be relatively time consuming, difficult and expensive to align and connect them to the flow switch 250, due to the extremely small size of the flexure 264, the inlet port 266, and the outlet ports 260. Such additional inlet conduits may also be undesirable because they may tend to trap a bubble when being filled with a liquid medication 12, which bubble might then be carried into the flow switch 250 and cause it to malfunction. When there is a zero driving pressure difference (P) of the medication 12 across the flow switch 250, the flexure 264 is not bowed by the medication 12, and is essentially parallel to the inlet switch seat 256's top surface 270. However, during operation of the flow switch 250, as a driving pressure difference (P) of the medication 12 is applied across the flow switch 250, such as by pressurizing the source of the medication 12 with respect to the flow switch 250's outlet port 260, by any suitable means, the medication 12 flows through the inlet port 266; flows radially outwardly across the inlet valve seat 256's top surface 270 through the switch gap 268; flows through the outlet cavity 258; and flows out through the outlet ports 260. As the driving pressure difference (P) of the medication 12 across the flow switch 250 is increased from zero, the medication 12 gradually forces the flexure 264 closer to the switch seat 268, thereby gradually decreasing the height of the switch gap 268 (and vice versa) . Then, at a predetermined overpressure of the medication 12, i.e., at a predetermined driving pressure difference switch point (P sw ) , the flexure 264 automatically begins an irreversible collapse that results in the flexure 264 being forced by the medication 12 against the inlet switch seat 256, and being held there by the medication 12, thereby automatically closing the switch gap 268, switching off the flow switch 250, and stopping the flow of the medication 12 through the flow switch 250. Then, when the driving pressure difference (P) across the flow switch 250 is decreased to less than the predetermined overpressure, i.e., is decreased to less than the predetermined driving pressure difference switch point ( p sw) ' the resiliency and elasticity of the flexure 264 cause it to automatically move away from the inlet switch seat 256, thereby automatically opening the switch gap 268, switching the flow switch 250 back on, and permitting the medication 12 to flow through the flow switch 250 once again. As a result, it is seen that, at a predetermined overpressure of the medication 12, i.e., at a predetermined driving pressure difference switch point (P sw ) , the flow switch 250 is automatically switched off, thereby stopping the flow of the medication 12 through the flow switch 250; and that the flow switch 250 will not switch on again and permit the medication 12 to flow through the flow switch 250 again until the overpressure condition is remedied i.e., until the driving pressure difference (P) is decreased to less than the driving pressure difference switch point (P sw ) • The above operation of the flow switch 250 is illustrated in the graph of Fig. 23, whose flow curve 272 is for the example flow switch 250 having the physical parameters that were set forth above. As seen in Fig. 23, the flow rate (Q) of the medication 12 through the flow switch 250 increases as a function of the driving pressure difference (P) across the flow switch 250, up to the predetermined driving pressure difference switch point ( p sw) °f about 6.2 mm Hg. At the predetermined driving pressure difference switch point (P sw ) of about 6.2 mm Hg, the flow switch 250 automatically switches off, and the flow rate (Q) drops to zero as the flexure 264 is forced against the inlet switch seat 256, and held there, by the medication 12. When the flow switch 250 has switched off, a high static pressure will occur across the switch 250, since it is now the primary resistance to the flow of the medication 12. Another way of interpreting the flow curve 272 is that as the flow rate (Q) of the medication 12 through the flow switch 250 increases, the driving pressure difference (P) across the flow switch 250 increases as a function of the flow rate (Q) , up to a predetermined flow rate switch point (Q sw ) of about 575 μL/day. At the predetermined flow rate switch point (Q sw ) of about 575 μL/day, the flow switch 250 automatically switches off, and the flow rate (Q) drops to zero as the flexure 264 is forced against the inlet switch seat 256, and held there, by the medication 12. The type of response curve 272 shown in Fig. 23 is highly desirable for many applications where, if the flow rate (Q) or the driving pressure difference (P) of the medication 12 exceeds a predetermined nominal limit, such as due to an overpressure in the supply of the medication 12, there may be undesirable consequences. For example, if the outlet for a reservoir in a medication delivery device for the medication 12 was equipped with a flow switch 250, then medication delivery device may be designed for nominal operation below a predetermined flow rate switch point (Q sw ) , or below a predetermined driving pressure difference switch point (P sw ) . Then, if either the predetermined medication flow rate switch point (Q sw ) or the predetermined driving pressure difference switch point (P sw ) is exceeded, such as if a medical person accidentally overfilled the medication delivery device's reservoir, the flow switch 250 would switch off the flow of the medication 12 from the medication delivery device until the excessive driving pressure difference (P) was rectified. That would significantly reduce the possibility of injury or death to the patient due to an overdose of the medication 12 which might otherwise occur. Referring now to the graphs of Figs. 24 - 26, the thin plotted line 274 in each graph is for the example flow switch 250, having the physical parameters set forth above, except that its initial switch gap (at a zero driving pressure difference (P) across the flow switch 250) , is as indicated on the horizontal axis. The thick plotted line 276 in Figs. 24 - 26 is for the example flow switch 250, having the physical parameters set forth above, except that its inlet switch seat 256 has a diameter of 0.5 mm, and its initial switch gap (at a zero driving pressure difference (P) across the flow switch 250) , is as indicated on the horizontal axis. In Fig. 24, the lines 274, 276 are the plots of the flow rate switch points (Q sw ) for the flow switches 250 as a function of the initial switch gap 268 (at a zero driving pressure difference (P) across the flow switch 250) . As seen in Fig. 24, the flow rate switch points (Q sw ) for the flow switches 250 are primarily set by the initial switch gap 268; but that the diameter of the inlet switch seat 256 is also significant, even though not as important. Fig. 25 shows the driving pressure difference switch point (P s ) for the flow switches 250 as a function of the initial switch gap 268 (at a zero driving pressure difference (P) across the flow switch 250) . As seen in Fig. 25, the driving pressure difference switch points ( p sw) for the fl° w switches 250 are primarily set by the initial switch gap 268; but that the diameter of the inlet switch seat 256 is also significant, even though not as important. Fig. 26 shows the switch point deflection of the flexure 264 at its inlet port 266 (D sw ) for the flow switches 250 as a function of the initial switch gap 268 (at a zero driving pressure difference (P) across the flow switch 250) . The switch point deflection (D sw ) is measured as a fraction of the initial switch gap 268 (at a zero driving pressure difference (P) across the flexure 264) . As seen in Fig. 26, the switch point deflection (D sw ) is relatively constant over a range of values for the initial switch gap 268. The theory of operation of the flow switch 250, with its flow of the medication 12 through its switch gap 268 between its inlet switch seat 256 and its flexure 264, is similar to the theory of operation set forth above regarding the radial flow regulator 32 of Figs. 1 - 2, and the flow of the medication 12 through its regulator gap 48 between its regulator seat 42 and its flexure 28, except for those differences which will be made apparent by an examination of all of the Figures and all of the disclosures in this document. For example, the curvature boundary conditions on the flexure 264 differ from the curvature boundary conditions on the flexure 28, due to the flexure 264's inlet port 266. In addition, the switch action of the flow switch 250's flexure 264 may be attributable to the destabilization of the flexure 264 caused by at least two things acting in concert. First, the destabilization of the flexure 264 may be caused by the fact that the outlet cavity 258 is at one of the lowest pressures in the flow switch 250. Since the flexure 264's incremental face area over the outlet cavity 258 is a function of the square of the radius of the flexure 264, the flexure 264's incremental face area is the greatest over the outlet cavity 258. Thus, there is a destabilizing leverage action exerted by the medication 12 on the flexure 264 due to the driving pressure difference of the medication 12 between the flexure's top surface 265 and the inside of the outlet cavity 258. Second, the destabilization of the flexure 264 may also be assisted by the free rim of the flexure's inlet hole 266, which helps to permit the flexure 264 to change its position and snap against the inlet switch seat 256. On the other hand, in the radial flow regulator 32 the medication 12 is at a relatively higher pressure in the inlet channels 38 and in the inlet cavity 40, as compared to the pressure of the medication in the regulator gap 48 and the outlet cavity 52, where the incremental face area of the flexure 28 is the least. So the regulator 32's flexure 28 tends to not exhibit the snap action of the flow switch 250's flexure 264. From the disclosures in this document, it is possible to selectively design a flow switch 250 having any particular desired characteristic curve 272, 274, or 276; having any desired predetermined flow rate switch point rate (Q sw ) for the medication 12; and having any desired predetermined driving pressure difference switch point (P sw ) for the medication 12. This may be done by selectively adjusting one or more of the pertinent parameters, such as: (a) the stiffness, elasticity, resiliency, thickness, size and shape of the flexure 264; (b) the number, size and shape of inlet port 266; (c) the size and shape of the inlet switch seat 256 and its top surface 270; (d) the size, shape and number of the outlet cavity 158 and the outlet ports 260; (e) the height of the switch gap 268, when the driving pressure difference (P) across the flow switch 250 is zero; and (f) the driving pressure difference (P) across the flow switch 250. MICROMACHINED MEMBRANE FLOW SWITCH 250 (FIGS. 21 - 26): MANUFACTURE The manufacture of the flow switch 250 is similar to the manufacture of the one-way valve 300 of Figs. 19 - 20, except for those differences which will be made apparent by an examination of all of the Figures and all of the disclosures in this document. For example, the desired initial switch gap 268 (at a zero driving pressure difference (P) across the flexure 264) , may be obtained by using an etching process in which the inlet switch seat 256 is etched by an amount equal to the desired initial switch gap 268, while the substrate 252's top surface 278 is not etched at all. It is understood that the foregoing forms of the invention were described and/or illustrated strictly by way of non-limiting example. In view of all of the disclosures herein, these and further modifications, adaptations and variations of the present invention will now be apparent to those skilled in the art to which it pertains, within the scope of the following claims.

Claims: What is claimed is: 1. A micromachined flow switch for selectively controlling a fluid flow, wherein said flow switch comprises: a substrate, a membrane, and a switch gap; wherein said substrate comprises a mounting portion, an inlet switch seat, and outlet port means for permitting said fluid to flow from said inlet switch seat and out of said flow switch; wherein said membrane comprises a mounting portion, a resilient flexure which extends over at least a portion of said inlet switch seat, and an inlet port means, which is located over said inlet switch seat, for providing a fluid path from a source of said fluid to said inlet switch seat; wherein said switch gap is located between said flexure and said switch seat; wherein said membrane and said substrate are secured together at their respective said mounting portions; wherein, when a positive driving pressure difference of said fluid across said flow switch, which is less than a predetermined driving pressure difference switch point, is applied to a top surface of said flexure and to said inlet port means, said fluid flows into said flow switch through said inlet port means, flows radially outwardly across a top surface of said inlet switch seat through said switch gap; and flows out of said flow switch through said outlet port means; wherein, at said predetermined driving pressure difference switch point, said flexure automatically collapses against said inlet switch seat, to automatically close said switch gap, switch off said flow switch, and stop said fluid flow through said flow switch; and wherein, at a driving pressure difference across said flow switch which is less than said driving pressure difference switch point, said resilient flexure automatically moves away from said inlet switch seat, to automatically open said switch gap, switch said flow switch back on, and permit said fluid to flow through said flow switch once again. 2. The flow switch according to claim 1, wherein said inlet port means comprises an inlet port in said flexure. 3. The flow switch according to claim 2, wherein flexure, said inlet port and said inlet switch seat's top surface are cylindrically symmetrical. 4. The flow switch according to claim 1, wherein said outlet port means comprise an outlet cavity in said substrate; and wherein said outlet cavity at least partially surrounds said inlet switch seat. 5. The flow switch according to claim 4, wherein said outlet cavity is at least generally ring-shaped. 6. The flow switch according to claim 4, wherein said outlet port means further comprises at least one outlet port which is in fluid communication with said outlet cavity. 7. The flow switch according to claim 1, wherein, at driving pressure differences which are equal to, or higher than, said predetermined driving pressure difference switch point, said inlet switch seat supports at least a portion of flexure, to help prevent said flexure from being ruptured by said driving pressure differences which are equal to, or higher than, said predetermined driving pressure difference switch point. 8. The flow switch according to claim 1, wherein said substrate's and membrane's mounting portions are anodically bonded to each other. 9. The flow switch according to claim 1, wherein said flow switch comprises at least one exposed portion which is exposed to said fluid during operation of said flow switch; wherein said flow switch further comprises a corrosion- resistant layer on at least part of said exposed portion; and wherein said corrosion-resistant layer is anodically bonded to said exposed portion. 10. The flow switch according to claim 9, wherein said corrosion-resistant layer comprises an oxide of a transition metal selected from the group consisting essentially of titanium and zirconium. 11. The flow switch according to claim 9, wherein said corrosion-resistant layer is located on at least part of said inlet switch seat's top surface; and wherein said corrosion-resistant layer on said inlet switch seat's top surface serves the dual functions of helping to prevent corrosion of said inlet switch seat's top surface, and helping to prevent a bottom surface of said flexure from being anodically bonded to said inlet switch seat's top surface. 12. A method for manufacturing a flow switch, wherein said flow switch comprises: a substrate, a membrane, and a switch gap; wherein said substrate comprises a mounting portion, an inlet switch seat, and outlet port means for permitting said fluid to flow from said inlet switch seat and out of said flow switch; wherein said membrane comprises a mounting portion, a resilient flexure which extends over at least a portion of said inlet switch seat, and an inlet port means, which is located over said inlet switch seat, for providing a fluid path from a source of said fluid to said inlet switch seat; wherein said switch gap is located between said flexure and said switch seat; wherein, when a positive driving pressure difference of said fluid across said flow switch, which is less than a predetermined driving pressure difference switch point, is applied to a top surface of said flexure and to said inlet port means, said fluid flows into said flow switch through said inlet port means, flows radially outwardly across a top surface of said inlet switch seat through said switch gap; and flows out of said flow switch through said outlet port means; wherein, at said predetermined driving pressure difference switch point, said flexure automatically collapses against said inlet switch seat, to automatically close said switch gap, switch off said flow switch, and stop said fluid flow through said flow switch; and wherein, at a driving pressure difference across said flow switch which is less than said driving pressure difference switch point, said resilient flexure automatically moves away from said inlet switch seat, to automatically open said switch gap, switch said flow switch back on, and permit said fluid to flow through said flow switch once again; and wherein said method comprises the steps of: micromachining at least a portion of at least one of said inlet and outlet port means, by etching at least a portion of at least one of said inlet and outlet port means into said flexure and said substrate, respectively; and securing said membrane's and substrate's mounting portions together. 13. The method according to claim 12, wherein said inlet port means comprises an inlet port in said flexure; and wherein said method further comprises the step of micromachining at least a portion of said inlet port into said flexure, by etching at least a portion of said inlet port into said flexure prior to performing said securing step. 14. The method according to claim 12, wherein at least a portion of said substrate's mounting portion is higher than said inlet switch seat's top surface, to produce a height difference between said inlet switch seat's top surface and at least a portion of said substrate's mounting portion; wherein said height difference is at least about equal to said switch gap; and wherein said method further comprises the step of micromachining at least a portion of said height difference, by etching away at least a portion of said inlet switch seat's top surface prior to performing said securing step. 15. The method according to claim 12, wherein said outlet port means comprises an outlet cavity in said substrate; and wherein said method further comprises the step of micromachining at least a portion of said outlet cavity into said substrate, by etching at least a portion of said outlet cavity into said substrate prior to performing said securing step. 16. The method according to claim 12, wherein said securing step comprises anodically bonding said substrate's and membrane's mounting portions together. 17. The method according to claim 12, wherein said method further comprises the steps of applying at least one layer of at least one corrosion-resistant material to at least a portion of said flow switch; and securing said layer of at least one corrosion-resistant material to said flow switch by using anodic bonding. 18. The method according to claim 17, wherein said steps of securing said membrane to said substrate and of securing said at least one layer of at least one corrosion- resistant material to said flow switch occur , simultaneously, and both of said steps of securing comprise anodic bonding. 19. The method according to claim 12, wherein said method further comprises the step using a laser for drilling said outlet port into said substrate; and wherein said laser, during said drilling, simultaneously forms at least a portion of said outlet port into a venturi-like shape. 20. The method according to claim 19, wherein said method further comprises the step of heating at least a portion of said substrate which is adjacent to said outlet port to about the anneal point of said substrate before performing said step of drilling, to help prevent said substrate from cracking during said step of drilling. 21. The method according to claim 12, wherein said method further comprises forming said membrane by the steps of providing a wafer of material having a first layer which is etchable by an etchant, and having a second layer which is not etchable by said etchant, wherein said second layer has a thickness about equal to the desired final thickness of said membrane; securing said second layer to said substrate during said step of securing said membrane to said substrate; and etching away at least a portion of said first layer with said etchant. 22. The method according to claim 21, wherein said inlet port means comprise an inlet port in said membrane; wherein both said first and second layers are etchable by a second etchant; and wherein said method further comprises micromachining said inlet port into said membrane by etching said inlet port into said wafer's second layer to a depth in excess of said desired final thickness of said membrane, prior to performing said securing step.

Inventors: LAWRENCE DALE M, SAASKI ELRIC W, LAWRENCE, DALE, M., SAASKI, ELRIC, W.
Applicants: RES INT INC, RESEARCH INTERNATIONAL, INC.
Application year: 1994
Main classification: F15C5
IPC codes: B01D61, B01D67, B01D69, B01D71, F04B43, F15C5, F16K99, G05D7